1. Field of the Invention
This invention relates to a method for treating at least one stream of aqueous fluid to a defined free residual level of one or more contaminants or other undesirable substituents by using the portable system and apparatus disclosed herein to control introduction of at least one oxidizing chemical, preferably chlorine dioxide, either alone or in combination with other additives. One preferred embodiment of the invention relates to a method for treating water intended for use in industrial, agricultural, food processing, oil and gas, or other applications. More specific examples of such uses include without limitation for treating industrial cooling water, HVAC cooling water, fruit and vegetable wash water, or poultry wash water, primary and secondary disinfecting of potable water, and treatment of aqueous fluids for subsurface applications such as disinfection, drilling, fracturing, well stimulation, sour well conversion, and well cleanout. One particularly preferred embodiment of the invention relates to a method for analyzing and treating source water and produced water (individually or collectively, “frac water”) used in hydraulic fracturing fluids (“frac fluids”) or aqueous fluids used in other processes for oil and gas wells.
2. Description of Related Art
The use of various oxidizing chemicals and non-oxidizing chemicals for treating water and, more particularly, for treating water used in frac fluids is well known. Because such fluids are routinely injected into well bores and subsurface formations, the possibility always exists that some leakage into the underground water table can occur. Some prior art systems and methods have disclosed introducing chlorine dioxide into fracturing fluids downstream of the fracturing fluid holding tanks (“frac tanks”) or forming it in situ downhole. These methods of addition have many disadvantages including, for example, less ability to control the chemical addition or to verify the additive concentration in the treated fluid, lack of portability, lack of a homogeneous blend, limited effectiveness due to pH of the water going downhole, and insufficient contact time or concentrations to kill bacteria. To applicants' knowledge, no one else presently treats the aqueous component of frac fluids upstream of the frac tanks.
A portable system, method and apparatus are therefore needed for effectively and economically treating source water and produced water to a defined free residual level of chlorine dioxide or other oxidizing chemical that ranges from about 0.25 to not greater than about 25 ppm depending upon application and situation. Other beneficial advantages achievable through use of the invention disclosed herein include, for example, the capability for reliably controlling the chemistry of and additive levels in treated water; for safely generating chlorine dioxide in a controlled environment; for independently recirculating, treating and adjusting the chemistry of and additive levels in fluids maintained in individual frac tanks; and, if a leak or overflow of a frac tank occurs, minimizing the amount of treating chemical that is released to the environment with far less harmful environmental impact than would likely be experienced if using traditional water treatment chemistries and methods.